A conventional method for forming nanoparticle coated substrate surfaces is physical evaporation in vacuum, such as to form metal (e.g., Pt) nanoparticles on a titania substrate for catalyst applications. It is known that metal nanoparticles formed using physical evaporation display sintering temperatures well below the melting point of the metal, such as <450° C. in the case of Pt which has a melting point of about 1773° C. This low sintering temperature behavior is generally a problem for catalysis applications such as for automotive catalysts, removal of NOx from turbines, as well as for the decomposition of H2SO4 for power generation, where the typical operating temperature is well above 450° C.
Sintering is known to increase the size of the nanoparticles, which can be problematic because for structure-sensitive catalytic reactions there is a known relation between the catalytic activity and the nanoparticle size, with smaller nanoparticles being more catalytically active. In addition, annealing generally results in encapsulation of the nanoparticles by a layer of the substrate material (e.g., titania), which reduces the catalytic activity. Accordingly, new methods and catalysts resistant to coarsening at higher temperature are needed.